答复: [PATCH] vgaswitchroo: set audio client id according to bound gpu client id

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Hi Lukas, 

Thanks to your explanation, and see comments in line.


Do you need to runtime resume the HDA controller even if user space isn't
streaming audio?  Why, and in which situation exactly?

Jim: OEM system uses pactl to queiry audio card and audio output sink, since the audio has power down by runtime pm, so the audio card and output sink are all unavailable. they could not select the available HDMI audio for audio playing.

You're saying above that the HDA controller isn't runtime resumed on
hotplug of a display.  Is that necessary to retrieve ELD or something?
I'm not sure if there's code in the HDA driver to acquire a runtime PM
ref on HPD, but maybe it's necessary.  Or maybe the code is there but
somehow no HPD interrupt is received by the HDA driver?

Jim: So far, I do not find any code about audio response HPD in kernel. the HPD interrupt will sent to user mode via uevent, not sure whether audio user mode driver can receive the event or not.

Thanks
JimQu

________________________________________
发件人: Lukas Wunner <lukas@xxxxxxxxx>
发送时间: 2018年7月9日 17:27
收件人: Qu, Jim
抄送: alsa-devel@xxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; Deucher, Alexander; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
主题: Re: [PATCH] vgaswitchroo: set audio client id according to bound gpu client id

On Mon, Jul 09, 2018 at 08:52:33AM +0000, Qu, Jim wrote:
> Now, I found the audio device will auto suspend even if the gpu is active,
> and if I plug in a HDMI device it also do not resume back.
>
> 1. Did you encounter similar issue before?
> 2. audio will auto suspend as default at beginning of boot, is it expect
> behaviour?

Yes, that's expected.  Once you start streaming audio to attached displays,
user space opens the codec device and this causes the HDA controller to
runtime resume.  If the discrete GPU is suspended at that moment, it will
be powered on and kept powered on as long as user space is streaming audio.

Do you need to runtime resume the HDA controller even if user space isn't
streaming audio?  Why, and in which situation exactly?

You're saying above that the HDA controller isn't runtime resumed on
hotplug of a display.  Is that necessary to retrieve ELD or something?
I'm not sure if there's code in the HDA driver to acquire a runtime PM
ref on HPD, but maybe it's necessary.  Or maybe the code is there but
somehow no HPD interrupt is received by the HDA driver?

Thanks,

Lukas
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